1. Field of the Invention
The present invention relates to a lens barrel in which a motor and a gear arranged to transmit the output of the motor to a part to be driven such as a rotating tube of the lens barrel are incorporated, and an optical apparatus having such a lens.
2. Description of Related Art Many of lens-interchangeable type cameras or compact cameras such as lens-shutter type cameras are arranged these days to have an automatic focusing function. In the case of lens-interchangeable single-lens reflex cameras, two methods for automatic focusing have been known. In one method, an automatic focusing motor is disposed inside a camera body and the output of the motor is transmitted through a coupler of a mount part to a distance ring of the lens barrel. In the other method, a motor unit composed of an automatic focusing motor and a reduction gear, etc., is disposed within a lens barrel and electric power is supplied from a camera body through a mount part to the motor unit.
The method of having an automatic focusing motor or a motor unit disposed within an interchangeable lens barrel has such an advantage that the speed of driving a moving lens for automatic focusing is not affected by the load (weight) of the moving lens. However, this method is detrimental to a reduction in size of the lens barrel.
In the case of a zoom lens, each lens group is arranged to be moved by transmitting rotation or a rectilinear motion of a zoom operation ring, through a roller which fittingly engages a cam groove or a rectilinear motion groove or through a cam follower which abuts on a cam face, to a movable lens-group holding frame.
In a known structural arrangement, the cam groove and the rectilinear motion groove and a roller fittingly engaging these two grooves for moving the movable lens-group holding frame in the direction of the optical axis or the cam face and the cam follower abutting on the cam face are formed at two symmetric positions which are spaced 180 degrees. According to this arrangement, however, the movable lens-group holding frame tends to be caused to slant by a fitting play between the roller and the cam groove or the rectilinear motion groove or by an abutment play between the cam follower and the cam face. The optical performance of the interchangeable lens barrel, therefore, tends to be affected by the play. To minimize the adverse effect of the play, it has been widely practiced to have these parts arranged at three equally spaced positions at intervals of 120 degrees, instead of two positions.
Further, the above-stated cam arrangement requires the cam part to be finished at a high rate of precision. To meet this requirement, many processes are necessary for metal machining. In view of that, these parts are more often formed by molding than by metal machining as the former requires simpler processes than the latter.
FIG. 1 is a vertical sectional view showing a conventional lens barrel. FIG. 2 is a development view of the essential parts of the same lens barrel. Referring to FIGS. 1 and 2, a fixed tube 51 is formed in one body with a lens mount which is provided for mounting the lens barrel on a camera body. A zoom operation ring 52 is fitted on the fore end outer side of the fixed tube 51 and is arranged to be rotatable at a fixed position by means of a shaft screw 53. A zoom rubber piece 54 is applied to the outer side of the zoom operation ring 52.
A first cam tube 55 is connected to the zoom operation ring 52 with a screw 65 to have its motion restricted in the direction of optical axis but is arranged to be rotatable with respect to the fixed tube 51. Several lead cams 55a and 55b which are in a convex, linear shape or a non-linear shape are formed on the inner side of the first cam tube 55.
A first lens frame member 56 has cam followers 56a and 56b which are of a concave shape and are fitted on the lead cams 55a and 55b and cutouts 56c and 56d which are of an approximate U shape and arranged on the outer side of the first lens frame member 56. Rectilinear motion guide members 57 are secured to the fixed tube 51 at one end of them and fitted in the cutouts 56c and 56d in the direction of the width of the lens barrel.
A second cam tube 58 has protruding cams 58b of an approximately helical shape arranged on its inner side to engage the cam followers 55c and 55d which are provided on the outer side of the first cam tube 55. A projection 58a is formed on the rear end outer face of the second cam tube 58 and engages the rectilinear motion guide groove 51a provided in the fixed tube 51.
A second lens frame member 59 has a helicoid 59a arranged on its inner side to be helicoid-coupled with a helicoid 58c formed on the fore end outer side of the second cam tube 58. Reference numeral 60 denotes a third lens frame member. Reference numeral 61 denotes a motor-driven diaphragm device.
An automatic focusing motor unit 62 has an automatic focusing motor (DC motor) 62a mounted thereon and is provided with a focus gear 62b. The focus gear 62b is in mesh with a gear (not shown) which is disposed within the second lens frame member 59. When the motor 62a is caused to rotate, a lens group which is carried by the second lens frame member 59 moves in the direction of the optical axis together with the second lens frame member 59 to perform a focusing action.
FIG. 3 is a plan view showing the automatic focusing motor unit 62 as viewed from on the side of the fixed tube 51. As shown, the motor unit 62 is composed of a plurality of reduction gears 62d and an idler gear 62c. These gears are arranged within a phase range of about 180 degrees.
In FIGS. 1 and 2, reference numeral 63 denotes a circuit board arranged to drive the automatic focusing motor 62a and the motor-driven diaphragm device 61. A lens microcomputer 63c is arranged on the circuit board 63 to receive electric power and information about a stopped-down amount of the diaphragm, a driving amount for focusing, etc., from a camera microcomputer which is disposed on the side of the camera body through a contact block 63a.
With the lens barrel arranged in this manner, when the zoom operation ring 52 is rotated, the first cam tube 55 rotates in the same direction and to the same extent as the rotation of the zoom operation ring 52. When the first cam tube 55 rotates, the first lens frame member 56 is moved along the rectilinear guide members 57 in the direction of the optical axis through the cam followers 56a and 56b which are in fitting engagement with the lead cams 55a and 55b formed on the inner side of the first cam tube 55. The fitting engagement of the cam followers 55c and 55d of the first cam tube 55 with the approximately helical protruding cam 58b causes the second cam tube 58 to move straight along the rectilinear guide groove 51a provided in the fixed tube 51. Then, the second lens frame member 59 which is helicoid-coupled with the second cam tube 58 moves in the direction of the optical axis. A zooming action is thus performed accordingly as the first lens frame member 56 and the second lens frame member 59 move back and forth in the direction of the optical axis.
Further, the focus gear 62b which is thrust-restricted by the second cam tube 58 is arranged to move forward or backward in the same manner as the second cam tube 58. The focus gear 62b is thus arranged to be capable of transmitting the rotation of the motor 62a to the second lens frame member 59 in any region of zooming.
In the lens barrel shown in FIGS. 1 and 2, the automatic focusing motor unit 62 occupies a large phase range of 180 degrees. Therefore, the large (high) protruding elements 63c forming the circuit board 63 must be arranged within a limited space where they do not interfere with the automatic focusing motor unit 62. The limitation of the space restricts the design latitude for the circuit board 63 to necessitate it to be arranged in a multilayer shape, which has resulted in a cost increase.
Further, to avoid interference of the second cam tube 58 shown in FIG. 1 with the motor 62a or with the reduction gear 62d in a zooming region obtained when the second cam tube 58 is caused by zooming to come to a position 58f which is nearest to the fixed tube 51, it is necessary to provide two cutouts 58d and 58e in the second cam tube 58. However, the provision of the two cutouts 58d and 58e degrades the strength of the second cam tube 58.